Resources exist for software programmers and developers to create Internet compatible services, software, and applications (e.g., Microsoft .NET Virtual Machine). Different programming languages may be used in writing such services, software and applications. They usually require the use of many modules and/or components (e.g., .DLL, .EXE) for successful execution on a computer. According to the European Computer Manufacturer's Association (ECMA) standards in an ECMA-335 virtual machine (VM) these components are called assemblies. Assemblies are the basis for developing, deploying, and running applications. When an application is executed the VM should have the ability to locate the assemblies and resources necessary to run the application. One common approach is to store common assemblies in a centralized or global assembly cache (GAC) within the computer where the VM is installed. A global assembly cache allows assemblies to be shared by several applications on the computer. Most basic assemblies, for example, the .NET framework, are installed in the GAC. The GAC may also store multiple versions of code (e.g., different code versions, different code cultures versions). Assemblies within the GAC are resources that are also fully trusted as secure to run on a machine by all applications. However, an application does not necessarily have to be fully trusted to use the GAC. In such instances, a security manager prevents untrusted applications from accessing trusted items through a trusted GAC assembly via a stack walk, which checks every callers, from every assemblies, for the required permissions, or throw a security exception.
An application may be assigned a set of permissions corresponding to one or more code groups that the application belongs to based on application characteristics, known as evidence. Evidence includes, but is not limited to, name, publisher, and/or origin of the application. For example, code from the local computer may have unrestricted permissions and thus be fully trusted, whereas code from the Internet will receive limited permissions characterized by an Internet permissions set (e.g., partially trusted). FIG. 1 illustrates un-trusted, semi-trusted, and trusted applications according to known prior art systems. As shown, un-trusted applications may be from external network such as the Internet. Semi-trusted application may be from an internal network such as an intranet and trusted applications may be local to a computer.
The GAC employs a static immutable security policy wherein all assemblies require strongnames (e.g., need to be digitally signed) and are fully trusted to be shared or else they can not be placed in the GAC. To prevent malicious applications and/or code from accessing secure resources (e.g., assembly files in assembly cache), the assemblies stored in the GAC can not depend on assemblies outside the GAC, which could have less than full trust. Thus an application and/or code not having full trust does not receive the benefit of a shared cache system, rather, these applications store their respective assemblies in one or more private, and often unshared, assembly directories. This can create inefficient use of memory (e.g., small devices like cellphones) and versioning problems.
As developers begin to create applications and web services with code executed from a partially trusted context or called by partially trusted code, there is no present way to increase efficiency in addressing commonly shared assemblies for less than fully trusted application code and/or assemblies. Multiple GAC's, also known as Multiple Assemble Caches (MAC) have been implemented in some VM (e.g. the Mono VM) to address separate assembly caches more consistently. This provides software to develop and run client and server applications on Linux, Solaris, Mac OS X, Windows, Unix, and/or other operating systems. Currently, however, multiple assembly caches are not addressed with respect to security—they are simply multiple instances of the original GAC concept. Therefore, there is no present way for securely increasing the efficiency of shared assemblies.